Aircrafts at takeoff, cruise and landing are prone to adverse airborne transparent or visible hazards. The source for these hazards is natural phenomenon, such as volcanic eruptions, atmospheric instability and jet streams. Most of the natural phenomena addressed here are not directly related to human activity. Yet, when it comes to aircrafts cruising at high altitudes, a wide spectrum of hazards is expected. These hazards range from bumpy flights, increased flight time, and higher fuel consumption to passenger injuries and aircraft crash risks.
Volcanic eruptions are worldwide phenomenon. Some active volcanoes are within the global flight routes of commercial aircrafts. A volcanic eruption is characterized by a large quantity of ash particles emitted and dispersed in the atmosphere. These micro-sized particles together with sand and dust can erode surfaces with which it comes into contact, and in more severe cases, can stall engines and compressors while penetrating into turbines and melting down rotating hot surfaces. Such events have led to major aircraft damages, and resulted in prolonged stoppages of aerial transportation.
Penetration of micro-particles into the aircraft cabin may risk the physical wellbeing of the aircraft passengers by adversely impacting the respiratory system, initiating lung diseases, or other health complications. A trail of volcanic ash is often accompanied with other more volatile materials, such as: acids and halogens. Sulfur dioxide (SO2) and sulfuric acid (H2SO4) are two examples of eruption by-products that pose high risk to the aircrafts and to passengers. Sulfuric acid (H2SO4) is a highly corrosive acid, which can gradually damage various aircraft components. In contrast, halogens exposed to UV sunlight can form radicals, which harm the ozone as well as other materials.
Although volcanic ash clouds are frequently monitored by aerial instruments, there is a lack of real time, en-route, altitude specific information, which is needed for rapid assessment and maneuvering.
The presence of water ice particles is common at cruising flight altitudes. At cruising altitudes, water can exist as an undercooled liquid without freezing. When an aircraft impacts a cloud of undercooled water, the undercooled water will undergo a sudden freezing and form into ice. As a consequence, ice will accumulate on the aircraft body, which elevates both the weight and air drag of the aircraft.
Aircrafts may experience turbulent shear forces when encountering vertical air currents of an approximate scale of 100 m to 2 km. One of the physical mechanisms for such shear forces stems from convectively induced turbulences around clouds and thunderstorms. These turbulences are visible to the naked eye and to onboard radars, and thus may be easily avoided. Another source for instability occurs in clear atmospheric conditions and is referred to as “clear air turbulence (CAT)”. It is assumed that man-made global warming partially contributes to these shear instabilities, which are expected to become more frequent in the impending future. Aircrafts encountering these invisible vertical shear forces may undergo sudden unpredictable movements and accelerations, resulting in the sensation of a “bumpy” flight, as well as potential injuries to aircraft crew members and passengers, and in extremes cases even fatalities. According to some estimates, aircrafts spend 3% of their cruising time in light intensity CATs and 1% of their cruising time in moderate CATs. Beyond their effect on passengers, CATs may also elicit structural damage of the aircraft and increase fuel consumption. To date, clear air turbulences are generally undetectable by onboard radars or satellites.
A current technology for turbulence detection is the enhanced X-band radar, with two main competitive systems: the Rockwell Collins WXR-700 series, and the Honeywell RDR-4 A/B series. These systems have two modes for detection of both wind shear and convective turbulence. However, based on market assessment of forward looking turbulence sensing systems, these systems were reported not to withstand expectations.
In recent years, Doppler LIDAR systems using phase information to determine vertical flow velocity of air lamella are under development, yet no commercial products are available. These systems rely on laser radiance emitted along the direction of flight route, monitoring the backscattering reflections of atmospheric molecules, such as carbon dioxide (CO2) and oxygen (O2). Two of the main disadvantages of LIDAR systems for CAT detection are narrow FOV, and limited laser power, resulting in limited detection range and angle. These drawbacks make it difficult for the pilot to obtain a complete image of the phenomenon and its extent. Lasers that operate at approximately 4-20 millijoules (mJ) allow for a detection range of about 5 miles, which is insufficient for risk assessment and decision making. Increasing the laser power, however, would lead to surplus weight as well as eye safety issues.
U.S. Pat. No. 7,109,912 to Paramore et al, entitled: “Weather radar hazard detection system and method”, discloses an aircraft weather radar system that includes a radar antenna, optical aircraft sensors, a database, a processing device, and a cockpit display. The processing device receives radar returns from the radar antenna and environmental variables from the aircraft sensors, and detects storm system hazards using a cell height parameter for a cell. The cell height parameter is determined by determining a direction to the cell using the environmental variables, and a range to the cell using the radar returns. The storm system hazards are displayed using an iconal or textual representation. The hazards may include: overshooting tops, vertical development, hail, vaulted thunderstorms, air mass stability, or cell growth rate.
U.S. Pat. No. 5,357,263 to Fischer et al, entitled: “Display instrument for aircraft for showing the aircraft orientation, particularly the rolling and pitching position or the flight path angle”, is directed to a head-up display of an aircraft which displays symbol features representative of the aircraft position in the exterior field of view of the pilot. The symbol features include a symbol stabilized in an earth-fixed manner for showing the true horizon position, as well as symbols representing the rolling angle, pitching angle, or flight path angle of the aircraft. A display of the attitude is generated by means of a reference symbol representing the aircraft and an information symbol which changes with respect to the reference symbol in its position and shape, and is dependent on the rolling angle and pitching angle or path angle.
U.S. Patent Application No. 2010/0231705 to Yahav et al, entitled: “Aircraft landing assistance”, discloses an enhanced vision system for assisting aircraft piloting. An aircraft control operator sends flight instructions associated with an object of interest to a pilot wearing a head-mounted display (HMD). A visual representation of the flight instructions with the object of interest marked is generated, respective of a combined spatial and symbolic image viewed by the pilot on the HMD. The aircraft control operator receives from the pilot confirmation of the flight instructions by designating the marked object of interest on the combined spatial and symbolic image, where the designation is performed in conjunction with the line-of-sight of the pilot.